People’s shopping habits are changing because of live streaming as a new business context. Based on this context, this study explores the effect of influencer happiness intensity on audience purchasing using the hard archival data from TikTok, the world’s top live-streaming app in terms of downloads. The influencers’ facial happiness intensity, attractiveness score, and visual attributions of the live streaming room were extracted from the videos using a machine learning method, and the estimation model was built. The findings indicate an inverted U-shape relationship between influencer happiness intensity and audience purchase, with accessories having the highest sales volume and an influence happiness intensity of 0.43. The additional propensity score matching test provides causal evidence for the negative impact of influencers’ happiness intensity on sales volume after exceeding the peak intensity, which is the subject of this paper. Furthermore, we investigate the probable underlying mechanism of the influencer-audience interaction. It demonstrates that the danmaku quantity and quality will have a partial mediation effect in the process of influencer happiness intensity influencing sales volume. These findings aid live-streaming influencers and platforms in optimizing their marketing strategies.